Conventionally, industrial heat exchangers have been fabricated from metals. Such exchangers are relatively expensive because of the materials, complex design and the high costs for welding, assembly and other aspects of fabrication. The costs have been prohibitively expensive for installation in homes and non-industrial environments such as office buildings, particularly where the need is for heat exchange or heat exchange combined with ventilation including humidification or dehumidification.
In attempting to reduce the cost of heat exchangers for domestic and office building use, plastic materials have been utilized such as laminations of polyethylene film mounted within a wood housing and capable of heat exchange between inside and outside air when used in conjunction with ventilation of substantially air-tight homes, as described in Popular Science, October 1980, pages 77-80. Industrial heat exchangers have also incorporated plastic heat exchange surfaces, as reviewed in "Nonmetallic Heat Exchangers: A Survey of Current and Potential Designs for Dry-Cooling Systems", Electrical Power Research Instititute (EPRI), Palo Alto, Calif. 94304, 120 pages particularly Sections 3, 4 and 5, and in U.S. Pat. Nos. 3,256,930 to Norback, 3,489,209 to Johnson and 4,286,365 to Creighton. The heat exchanger designs of the foregoing publications and patents include capillary falling water film between non-rigid sheets of plastic film, plastic plate types similar in function to tubular solar collectors, aluminum plates laminated between plastic sheets, corrugated plastic tubing, and various smooth, bare, parallel plate exchangers utilizing air flow between the plates.
All of the foregoing designs involve the use of low cost plastic and other materials, but the high labor cost for fabrication of these somewhat complex designs remains a deterrent for their use in other than industrial applications, such as the chemical process and electrical power industries.